Manufacturing Technology of Lined Composite Stainless Steel Seamless Pipes Using Novel Hydraulic Expansion Method

Overview of the Study

This 2002 publication by Wang Xuesheng (Shanghai Jiao Tong University) and Li Peining and Hui Hu (East China University of Science and Technology) addresses a critical challenge in the fabrication of lined composite seamless steel pipes for chemical equipment and piping systems. The core innovation lies in the application of a novel hydraulic expansion method to achieve mechanical bonding between a carbon steel base pipe and a stainless steel liner tube, eliminating the need for traditional welding overlay on long pipe sections. The work was published in the context of chemical equipment and piping technology, where corrosion-resistant linings are essential for handling aggressive process media.

Core Technical Approach

The hydraulic expansion method relies on applying controlled internal pressure to a stainless steel liner tube that has been inserted into a slightly oversized carbon steel base pipe. The differential in yield strengths and the controlled plastic deformation of the base pipe create a permanent interference fit at the interface. This approach offers several advantages over welding-based cladding for seamless pipe applications, including the absence of heat-affected zones, no risk of intergranular corrosion at the bond line, and the ability to process long pipe lengths without seam weld discontinuities.

The key process parameters governing the success of this method include:

Interface Bond Mechanism

The bond strength achieved through hydraulic expansion is primarily mechanical in nature, arising from the radial compressive stress at the interface after the expansion tool is withdrawn. The elastic recovery of the base pipe creates a clamping force on the liner tube, generating a frictional bond that can resist axial tensile loads, internal pressure, and thermal cycling. Metallographic examination typically reveals a clean interface with no intermetallic compounds, which is a significant advantage over welded overlays where diffusion bonding or intermetallic formation can compromise long-term durability.

Engineering Considerations and Defect Analysis

In practical manufacturing, several defect modes must be anticipated and controlled:

• Liner wrinkling or buckling: Occurs when the expansion ratio is insufficient relative to the liner's buckling resistance, particularly for thin-walled liners with high aspect ratios. Countermeasures include optimizing the liner-to-base diameter ratio and ensuring uniform wall thickness of the liner tube.
• Base pipe splitting: Results from excessive expansion pressure causing the outer surface of the base pipe to yield and crack. This is particularly likely in high-strength base pipes or those with pre-existing surface defects.
• Incomplete bonding: Localized regions where the interference fit is insufficient, often caused by eccentricity between the liner and base pipe or non-uniform wall thickness of the base pipe.
• Residual stress effects: The expansion process introduces significant residual stresses in both the base pipe and the liner. The base pipe experiences residual compressive stress on the inner surface and tensile stress on the outer surface, while the liner experiences residual compressive hoop stress. These residual stress distributions must be evaluated for their impact on fatigue life and pressure containment.

Process Optimization and Quality Control

A systematic approach to process optimization involves the following steps:

1. Material selection and characterization: Determine the mechanical properties, chemical composition, and microstructure of both the base pipe and liner materials. The stainless steel liner (typically 304 or 316L) must have adequate ductility to accommodate plastic deformation without cracking.
2. Finite element simulation: Use elastic-plastic finite element analysis to predict the required expansion pressure, the resulting interface pressure, and the residual stress distribution. This allows optimization of the expansion ratio to achieve the target bond strength while avoiding liner failure.
3. Process parameter calibration: Conduct trial expansions on coupon specimens to establish the relationship between expansion ratio and bond strength, and to identify the onset of liner wrinkling or base pipe splitting.
4. Non-destructive inspection: Apply ultrasonic testing (UT) to detect incomplete bonding or delamination at the interface. Magnetic particle testing (MT) of the outer surface can reveal base pipe cracks.
5. Destructive verification: Perform axial pull-out tests and ring shear tests on witness samples to verify that the achieved bond strength meets the design requirements.

Integration with Engineering Practice

In chemical plant piping systems, lined composite seamless pipes are preferred over welded overlays for several reasons. The absence of a heat-affected zone eliminates concerns about sensitization of the stainless steel liner, which is particularly important in chloride-containing environments where intergranular corrosion is a significant degradation mechanism. Additionally, the hydraulic expansion method preserves the full mechanical integrity of the stainless steel liner, ensuring that the corrosion resistance is not compromised by dilution or microstructural changes.

However, the method has certain limitations that must be considered in engineering design. The bond strength is pressure-dependent and can be affected by sustained high-temperature service, where thermal expansion mismatch between the carbon steel and stainless steel may reduce the interface pressure. For applications involving cyclic pressure loading, fatigue evaluation of the bond interface is essential. The method is also less suitable for very large diameter pipes where the required expansion pressures become impractically high.

Key Questions and Reflections

A critical question arising from this work is the long-term durability of the mechanical bond under thermal cycling conditions. While the method produces an excellent initial bond, the differential thermal expansion between carbon steel and stainless steel can lead to progressive loosening of the fit at elevated temperatures. For applications involving sustained temperatures above 200°C, a hybrid approach combining hydraulic expansion with localized welding at the pipe ends may be necessary to ensure long-term integrity.

Another important consideration is the scalability of the method to large-diameter pipes. The required hydraulic pressures increase with the square of the pipe diameter, which imposes practical limits on the equipment capacity. For pipes with diameters exceeding 500 mm, alternative methods such as explosion cladding or roll-bonding may be more appropriate.

This study represents a significant contribution to the field of mechanical bonding for lined pipes, offering a practical alternative to welding-based cladding for seamless pipe applications. The key insight is that mechanical interference bonding, when properly designed and executed, can achieve bond strengths comparable to welded overlays while preserving the full corrosion resistance of the liner material. Future work should focus on extending the service temperature range and developing reliable non-destructive evaluation techniques for bond quality verification in the field.